[Fetch] Support various operations after reading data partially.

Source/modules/fetch/Body.h

Index: Source/modules/fetch/Body.h
diff --git a/Source/modules/fetch/Body.h b/Source/modules/fetch/Body.h
index 7bc07b1cd318af97757144233aacd724fec7af6f..af9243898f20df90c289249dd75b532f10b696a4 100644
--- a/Source/modules/fetch/Body.h
+++ b/Source/modules/fetch/Body.h
@@ -56,7 +56,7 @@ public:
     bool streamAccessed() const;
 
     // Creates a new BodyStreamBuffer to drain the data from the ReadableStream.
-    BodyStreamBuffer* createDrainingStream(bool* dataLost);
+    BodyStreamBuffer* createDrainingStream();
 
     // ActiveDOMObject override.
     virtual void stop() override;